Pachycephalosaurus
}} Pachycephalosaurus is an extinct genus of ornithschian dinosaurs. It was a bipedal herbivore with an extremely thick skull roof, long legs and short arms. It lived during the Late Cretaceous lived with other North American dinosaurs such as Triceratops and Tyrannosaurus. The fossil can be found in both the United States and Canada. The thick skull domes of Pachycephalosaurus and related genera gave rise to the theory that pachycephalosaurs used their skulls to fight each other. This theory has been disputed in the past few years. Description The anatomy of Pachycephalosaurus is not well known, as only its skull has been described. Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10. Pachycephalosaurus is famed for its large dome on top of its skull, made of up to 10 in thick bone, which kept its tiny brain safe. The dome's rear aspect was edged with bony knobs and short bony spikes sticking up from the snout. The spikes were likely blunt, not sharp. The skull was short, with large, rounded eyes that faced towards the front, suggesting that the animal had good sight and was capable of binocular vision. Pachycephalosaurus had a small snout which ended in a sharp beak. The teeth were tiny, with leaf-shaped crowns. The head was supported by an "S"- or "U"-shaped neck. Carpenter, Kenneth (1 December 1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (pdf). Contributions to Geology 32 (1): 19–25. Pachycephalosaurus was likely bipedal and was the largest in the group family. It measured 15 to 16 feet long, stood 6 feet tall which is the same height as Deinonychus, and weighed 990 pounds.Paul, Gregory S. (2010). The Princeton Field Guide to Dinosaurs. Princeton, NJ: Princeton University Press. p. 244. ISBN 978-0-691-13720-9. Based on other dome-headed dinosaurs, it probably had a short, thick neck, short fore limbs, a strong body, long hind legs and a thick tail, which was likely held stiff by ossified tendons. Organ, Christopher O.; Adams, Jason (2005). "The histology of ossified tendon in dinosaurs". Journal of Vertebrate Paleontology 25 (3): 602–613. doi:10.1671/0272-4634(2005)025[0602:THOOTI2.0.CO;2]. Retrieved 2008-06-10. History Remains attributed to Pachycephalosaurus may have been found since the 1850s. As judged by Donald Baird, in 1859 or 1860 Ferdinand Vandiveer Hayden, an early fossil collector in the North American West, picked up a piece of bone close to the head of the Missouri River, from what is now known to be the Lance Formation in Montana. Baird, Donald (1979). "The dome-headed dinosaur Tylosteus ornatus Leidy 1872 (Reptilia: Ornithischia: Pachycephalosauridae)". Notulae Naturae 456: 1–11. This specimen was described by Joseph Leidy in 1872 as from the dermal plate of a reptile or an armadillo-like animal. Leidy, Joseph (1872). "Remarks on some extinct vertebrates". Proceedings of the Academy of Natural Sciences of Philadelphia, 1872: 38–40. Its true nature was not found until Baird restudied it a century later and identified it as a bone from the back of the skull of Pachycephalosaurus, including a set of bony knobs that matched those found on other specimens of Pachycephalosaurus. Baird, Donald (1979). "The dome-headed dinosaur Tylosteus ornatus Leidy 1872 (Reptilia: Ornithischia: Pachycephalosauridae)". Notulae Naturae 456: 1–11. Since the name Tylosteus predates Pachycephalosaurus, according to the International Code of Zoological Nomenclature it should be used. In 1985, Baird successfully petitioned to have Pachycephalosaurus used in lieu of the old Tylosteus as the latter name had not been used for more than 50 years, was based on undiagnostic materials, and had poor information. ICZN Opinion 1371, "[http://www.archive.org/stream/bulletinofzoolog43inte/bulletinofzoolog43inte_djvu.txt Pachycephalosaurus Brown & Schlaikjer, 1943 and Troodon wyomingensis Gilmore, 1931 (Reptilia, Dinosauria): Conserved.]" Bulletin of Zoological Nomenclature, 43 (1): April 1986. Glut, Donald F. (1997). "Pachycephalosaurus". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 664–668. ISBN 0-89950-917-7. This may not be the end; Robert Sullivan suggested in 2006 that the fossil is more like the bone of Dracorex than that of Pachycephalosaurus.Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10. The could be of little importance, though, if Dracorex is deemed a youn Pachycephalosaurus, as has been recently proposed. Stokstad, Erik (2007). "SOCIETY OF VERTEBRATE PALEONTOLOGY MEETING: Did Horny Young Dinosaurs Cause Illusion of Separate Species?". Science 318 (5854): 1236. doi:10.1126/science.318.5854.1236. PMID 18033861. P. wyomingensis, the type and sole valid species of Pachycephalosaurus so far, was named by Charles W. Gilmore in 1931. He coined it for a skull from the Lance Formation of Niobrara County, Wyoming. Gilmore assigned his new species to Troodon as T. wyomingensis. Gilmore, Charles W. (1931). "A new species of troodont dinosaur from the Lance Formation of Wyoming". Proceedings of the United States National Museum 79 (9): 1–6.At the time, paleontologists thought that Troodon, then known just from teeth, was the same as Stegoceras, which had similar teeth. Therefore, what are now known as pachycephalosaurids were assigned to the family Troodontidae, a wrong idea not corrected until 1945, by Charles M. Sternberg. Glut, Donald F. (1997). "Troodon". Dinosaurs: The Encyclopedia. Jefferson, North Carolina: McFarland & Co. pp. 933–938. ISBN 0-89950-917-7. Classification The pachycephalosaur Dracorex may actually be a Stygimoloch or Pachycephalosaurus in which the dome and horns are not well-developed, either because the animal was a juvenile or a female. This idea was backed up at the 2007 annual meeting of the Society of Vertebrate Paleontology.Erik Stokstad,"SOCIETY OF VERTEBRATE PALEONTOLOGY MEETING: Did Horny Young Dinosaurs Cause Illusion of Separate Species?", Science Vol. 18, 23 Nov. 2007, p. 1236; http://www.sciencemag.org/cgi/content/full/318/5854/1236 Jack Horner of Montana State University showed proof, from study of the skull of the one existing Dracorex specimen, that this dinosaur may well be a young form of Stygimoloch. Plus, he showed data that shows both Stygimoloch and Dracorex may be young forms of Pachycephalosaurus. Horner and M.B. Goodwin published their findings in 2009, that showed the spike/node and skull dome bones of all three 'species' have extreme plasticity, and that both Dracorex and Stygimoloch are just known from young specimens while Pachycephalosaurus is just known from adult specimens. These notes, as well as the fact that all three forms lived in the same time and place, lead them to think that Dracorex and Stygimoloch were just young Pachycephalosaurus, which lost spikes and grew domes as they aged.Horner J.R. and Goodwin, M.B. (2009). "Extreme cranial ontogeny in the Upper Cretaceous Dinosaur Pachycephalosaurus." PLoS ONE, 4(10): e7626. Online full text A 2010 study by Nick Longrich and colleagues also backed up the theory that all flat-skulled pachycephalosaurs were young, suggesting that flat-skulled forms like Goyocephale and Homalocephale represent juveniles of dome-skulled adults.Longrich, N.R., Sankey, J. and Tanke, D. (2010). "Texacephale langstoni, a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA." Cretaceous Research, . doi:10.1016/j.cretres.2009.12.002 Paleobiology Nearly all Pachycephalosaurus fossils came from the Lance Formation and Hell Creek Formation.Sullivan, Robert M. (2006). "A taxonomic review of the Pachycephalosauridae (Dinosauria:Ornithischia)". Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35: 347–366. Retrieved 2010-11-10. Pachycephalosaurus co-existed with young pachycephalosaurs Dracorex and Stygimoloch. Other dinosaurs like Thescelosaurus, Edmontosaurus, Triceratops, Ankylosaurus, and the theropods Ornithomimus, and Tyrannosaurus shared its time and place.Weishampel, David B.; Barrett, Paul M.; Coria, Rodolfo A.; Le Loeuff, Jean; Xu Xing; Zhao Xijin; Sahni, Ashok; Gomani, Elizabeth, M.P.; and Noto, Christopher R. (2004). "Dinosaur Distribution". In: D.B. Weishampel, P. Dodson, and H. Osmólska (eds.) The Dinosauria (2nd edition). 517–606. ISBN 0-520-24209-2. Scientists once thought that Pachycephalosaurus and its relatives were like bighorn sheep or musk oxen; where males would ram each other with head butts. It was also believed that they would make their head, neck, and body horizontally straight, to transmit stress during the crash. But it is now believed that the pachycephalosaurs could not have used their domes in this way. First, the skull roof could not have adequately sustained impact associated with such shock. Also, there is no evidence of scars or other harm on fossils of Pachycephalosaurus skulls. Furthermore, the dorsal vertebrae show that the neck was carried in an "S"- or "U"-shaped curve, not a straight direction, and thus to weak for direct clash of heads. Lastly, the rounded shape of the skull would lessen the contacted surface area during head-butting, resulting in misses. It is more likely that the Pachycephalosaurus and other pachycephalosaurs hit each other in the flanks. In this setting, an individual may have stood parallel or faced a rival directly, using intimidation displays to rival. If intimidation failed, the Pachycephalosaurus would bend its head down and to the side, and strike the rival pachycephalosaur on its flank. This hypothesis is back up by the broad width of most pachycephalosaurs, a trait that would have kept vital organs from harm. The flank-butting theory was first proposed by Sues in 1978, and expanded by Ken Carpenter in 1997.Carpenter, Kenneth (1 December 1997). "Agonistic behavior in pachycephalosaurs (Ornithischia: Dinosauria): a new look at head-butting behavior" (pdf). Contributions to Geology 32 (1): 19–25. Diet Scientists do not yet know what these dinosaurs ate. Having small, ridged teeth they could not have chewed tough, fibrous plants as effectively as other dinosaurs of the same time. It is assumed that pachycephalosaurs lived on a mixed diet of leaves, seeds, fruit and insects. The sharp, jagged teeth would have been very effective for shredding plants. Pachycephalosaurus in The Land Before Time Pachycephalosaurus are commonplace as background characters in The Land Before Time, and have been referred to by a number terms during the series, including "crownhead", "lizardhead", and "bonehead". They first appear in the original , in the form of a trio of hostile creatures who attack Cera. They are frightened away when the other kids, disguised as a tar monster, enter the cave the attack occurs in. Though not given descriptive names in the final film, they are referred to as "lizard-heads" in The Land Before Time: The Illustrated Story and Friends in Need, while Pachycephalosaurus in an earlier scene in The Illustrated Story and in the script for The Land Before Time are referred to as "crown-heads". More Pachycephalosaurus appear in in The Land of Mists, wherein one pachycephalosaur frightens a flock of Struthiomimus into a river and threatens the main characters, before noticing another member of its kind challenging it to a fight. The two Pachycephalosaurus butt heads, and are not seen again for the rest of the film. No terms are used to describe them. In , Pachycephalosaurus begin to appear in crowd shots taking place in the Great Valley, and depictions of them as savages are halted. In in particular, wherein the end credits tag the genus with the term "bonehead", [[Female Bonehead|a Pachycephalosaurus]] partakes in the plan to hunt down the Tinysauruses after Littlefoot blames them for the Tree Sweet Tree's leaves all being eaten before Nibbling Day. Pachycephalosaurus also prominently appear in the television series, where, though they themselves are not given descriptive terms, fellow pachycephalosaurs Stegoceras are referred to as "domeheads". Gallery MoreDomeheads.jpg Domehead6.jpg Crownheads fleeing.jpg LBT Pachycephalosaur.png LBT Pachycephalosaurus.png Saurolophus headshot.png|Pachycepahlosaurus pair in the background. Pachycephalosaur3 Forbidden freindship.PNG Crown-heads.jpg Domehead LBT 5.png|Pachycephalosaurus in LBT Wannanosaurus.png|Baby Pachycephalosaurus during Flip, Flap and Fly. Vlcsnap-2018-11-20-11h05m18s743.png References External links *[http://www.dinodictionary.com/dinos_p.asp#PACHYCEPHALOSAURUS Pachycephalosaurus in the Dinodictionary] *[http://animals.nationalgeographic.com/animals/prehistoric/pachycephalosaurus-wyomingensis.html Pachycephalosaurus wyomingensis] from National Geographic Online *TEDx talk by Jack Horner on shape-shifting dinosaur skulls and dinosaur misclassification. Category:Twofooters Category:Dinosaurs Category:Land Before Time species Category:Boneheads Category:Cretaceous Category:Leaf Eaters Category:Land Before Time I introductions Category:Land Before Time IV: Journey Through the Mists introductions Category:Pachycephalosauridae Category:Pachycephalosaurinae Category:‬Pachycephalosaurini Category:North American Dinosaurs Category:American Dinosaurs